This invention relates in general to drum support apparatus and more specifically to a drum supporting hub, a drum assembly containing the hub and method for fabricating the drum assembly.
Electrostatographic imaging drums are well known in the art. These drums comprise a hollow cylindrical substrate and at least one electrostatographic coating. These drums are usually supported by a hub held in place at the end of each drum by a flange extending from the hub into the interior of the drum and retained in place by an interference fit and/or an adhesive. An axle shaft through a hole in the center of each hub supports the hub and drum assembly. Since some electrostatographic imaging drums and their supporting hardware may have slight tolerance deviations or may become imperfect due to wear, these drums tend to wobble when rotated around their axle shaft. Such wobble is undesirable where precise spacing is required between the electrostatographic coating on the drum and various subsystems of the imaging system such as developing, cleaning and charging substations. In order to achieve uniform spacing between the imaging apparatus subsystems and the imaging surface of the drum, one may utilize spacing or support elements extending from the subsystems such as struts, shoes, or wheels which actually ride on the drum surface. Thus, any wobbling movement of the drum will merely allow the subsystem to to continue to maintain its position relative to the adjacent surface of the drum as the drum wobbles during rotation. The use of spacing or support elements extending from electrostatographic subsystems to ride directly on a drum surface is well known in the art and is disclosed, for example, in U.S. Pat. Nos. 3,869,203 and 3,998,184. The disclosures of these patents are incorporated herein in their entirety.
One common technique for fabricating these electrostatographic imaging drums involves dip coating the drum into a coating bath to form a dielectric layer for electrographic imaging members or to form at least one electrophotographic layer for electrophotographic imaging members. The electrophotographic imaging layer may be single electrophotographic imaging layer or comprise two or more layers such as a charge generation layer and a charge transport layer. All of these electrostatographic imaging layers are well known and conventional. During the dip coating process, one end of the drum substrate is vertically submerged with the axis of the drum substrate maintained in a vertical orientation until most or all of the external drum substrate surface is coated with the coating solution. Dip coating of electrostatographic imaging drums are well known in the art. Since the upper boundary of the applied coating layer tends to have a nonuniform thickness, the electrical properties thereat are also nonuniform. This problem is minimized by bringing the coating to the top of the substrate during dip coating so that the region actually utilized for electrostatic imaging is spaced away from the coating boundary. Since at least the bottom end of the substrate is coated and, in the latter situation, the upper end is also coated, difficulties are encountered when subsystems employed in cooperation with the electrostatographic imaging drum are spaced from the imaging surface of the electrostatic imaging drum by spacing means that ride on one or both ends of the drum to achieve more accurate spacing tolerances. As described above, these spacing means achieve spacing tolerances by compensating for situations where the drum wobbles as it rotates.
The spacing means which ride on the surface of the drum usually comprise a strut fitted with a roller or low friction foot. Such spacing means are well known in the art and are described, for example, in U.S. Pat. Nos. 3,869,203 and 3,998,184, referred to above. As the drum is rotated through many imaging cycles, the spacing means causes erosion of the coating on the drum substrate in the regions contacted by the spacing means and the resulting eroded coating debris forms an undesirable dust which settles on critical surfaces within the machine such as the imaging surface, corona wires, optic system components, and the like. To avoid this problem, the coating on at least one end of the drum (if the other end remains uncoated) is removed prior to installation of the drum in an electrostatographic imaging machine such as a copier, duplicator, printer or the like. Attempts to remove the coating with the aid of solvents can cause solvent splashing or fumes which can damage areas of the coating which are to be subsequently utilized for imaging. Also, solvent removal is usually employed in combination with a wiping means such as a brush or pad which are unreliable and often fail to remove all of the coating material at the end of the imaging drum. Moreover, disposal or recovery of the solvent can be hazardous, time consuming and expensive. The coating can also be removed by use of a laser beam, but such laser systems are also complex and expensive. Moreover, the solvent/wiping or laser systems for removal of coatings are bulky and prevent achievement of high substrate population density for efficient coating and cleaning operations. Masking techniques may also be employed to remove deposited coatings from the ends of drum substrates. More specifically, a masking tape may be applied to the end or ends of a drum substrate to allow the coating to deposit on the tape instead of on the underlying substrate. The coating deposited on the tape is removed when the tape is stripped from the substrate after the coating operation. These operations all adversely affect production costs, factory floor space requirements and the like. After the coating material has been removed from at least one end of a coated drum, a hub is installed to support the drum on an axle shaft for rotation in an electrostatographic imaging machine.
The requirement that the ends of a electrostatographic imaging drum carry a bare strip at each end reduces the amount of productive area on the exterior surface of the drum available for forming images. Thus, the drum is usually longer than is actually needed for formation of electrostatographic images. This increases drum material costs and leads to greater packaging, shipping and storage space requirements and expenses. Moreover, electrostatographic coating material is wasted because it is deposited at one or both ends of the drum and thereafter removed to provide a suitable surface for the subsystem support means.
When a bare strip is formed on the drum by removal of coatings adjacent to the end or ends of the electrostatographic imaging member to expose the underlying substrate, cycling of such an imaging member during an imaging process involving steps such as liquid development and wiping to clean the imaging surface tends to expose the edges of the electrostatographic coating, particularly any underlying more vulnerable layers, to solvent used in the liquid ink developer thereby causing deterioration of the layers and degradation of the imaging capabilities of the electrostatographic imaging member. Also, the bare strips are eroded by the spacing means during extensive image cycling and renders the used drum unsuitable for simple recycling.
Hubs have also been used which have a peripheral support surface to space subsystems from the imaging surface of a thin electroformed electrostatic imaging drum by allowing a subsystem spacing means to ride on the peripheral support surface or support ring of the hub. The hub is held in place by press fitting a flange extending from the hub into the interior of the drum. This type of hub is described in Japanese Patent Publication 58-87579, published May 5, 1983. However, the outermost periphery of the hub disclosed in Japanese Patent Publication 58-87579 is in the shape of a flange which extends above the surface of a thin-walled, electroformed tube. This hub flange abuts against the electroformed tube which has an outside diameter much smaller than the diameter of the hub flange. The corner formed at the intersection of the drum and the abutting flange can collect toner and other debris during image cycling until the accumulation of debris becomes so large that it dislodges and migrates to and contaminates critical components of the imaging system such as imaging surfaces, optical components, corona wires and the like. Cleaning the intersection with conventional cleaning devices can encounter difficulties such as collisions between the abutting flange of the hub and fragile cleaning blades. Repeated collisions will damage the cleaning blade, reduce its cleaning efficiency and shorten overall life.
Thus, there is a continuing need for improved photoreceptors that are more reliable and simpler to fabricate.